The present invention concerns a novel ablation catheter and, more particularly, a steerable catheter carrying a positional sensor for mapping.
Catheter ablation has become a well-known technique for treating various a flexible tubular electrode that is selectively extendable from a distal end of a catheter body, have been used in treating cardiac arrhythmias. An example of an ablation catheter system utilizing an extendable electrode is disclosed in Nelson et al. U.S. Pat. No. 5,800,428.
In treating tachyarrhythmias using cardiac ablation techniques, discrete, 4 or 8 mm electrodes are placed in the heart under fluoroscopic and electrophysiological guidance. By nature, these are not very precise location tools. Often, during these procedures, it is highly desirable to return to the location of a previous ablation and determine the effectiveness or completeness of a lesion. Because the area has been electrically damaged, EP signals are either non-existent or their amplitude has been reduced significantly to the point of being unusable. In addition, because fluoroscopy provides only a two dimensional view of a three dimensional space, returning within several millimeters to a previous location is not possible. Thus, it would be helpful to have a different means to establish the location of a catheter tip within a cardiac chamber. At least one technology exists in which a sensor is placed within the catheter structure and this sensor interacts with external devices to spherically triangulate and determine the position of the sensor. The accuracy of such methods in part depends on the proximity of the sensor to the tip.
One difficulty in attaching a sensor to current catheter designs is finding adequate space near the tip to place the sensor which in some case can be half the volume of the tip. In solid tip electrode designs, a mass of metal is needed to provide passive cooling during ablation. In cooled tip electrode designs, flow passages are needed to transport fluid to the distal regions of the tip. Because of inefficient cooling and resultant high flow rates, these passages consume most of the available space in both the tip electrode and shaft.
In Brucker et al. U.S. Pat. No. 5,643,197, a porous metal structure was designed to reduce the coolant flow to a fraction of the requirement for other tips. However, the mechanical integrity of the porous tip is predicated on having a thicker cross sectional area which precludes the placement of a sensor near the tip.
It is an object of the present invention to provide an ablation catheter in which a positioning sensor is efficiently located within the tip to provide information on the location of the catheter tip in the heart.
Another object of the present invention is to provide an ablation catheter in which there is an efficient flow of cooling fluid through the electrode tip while still providing an efficient location for the positioning sensor carried by the electrode.
A still further object of the invention is to provide an ablation catheter using an electrode which perfuses fluid to cool the tip and to form a protective layer which minimizes or eliminates contact with blood.
Another object of the present invention is to provide an ablation catheter in which there is an effective means to establish the location of the electrode tip within a cardiac chamber.
A further object of the present invention is to provide a catheter for creating a focal lesion using RF energy which utilizes an ablation electrode that provides efficient fluid disbursement and also efficient cooling of the electrode tip.
Other objects and advantages of the invention will become apparent as the description proceeds.
In accordance with the present invention, an ablation catheter is provided which comprises a steerable catheter including a distal portion and an ablation electrode carried by the distal portion. In one embodiment, the ablation electrode comprises a helically shaped tube and a positional sensor is located in the space defined by the helically shaped tube.
In one embodiment, the helically shaped tube has a proximal end and distal end, with the proximal end being coupled to a source of cooling fluid. The distal end is adapted to enable cooling fluid to flow between windings of the helically shaped tube, to form an insulating layer around the distal end to reduce impedance rises caused by blood coagulation.
In another embodiment, the helically shaped tube defines openings for exit of the cooling fluid as it passes through the tube. In that embodiment, the helically shaped tube may be wound so that each turn of the tube touches neighboring turns.
In the illustrative embodiments, the ablation catheter includes a proximal portion comprising a handle and a sliding mechanism for extending the distal portion.
In another embodiment, an ablation catheter is provided which comprises a steerable catheter including a distal portion with an ablation electrode carried by the distal portion. In this embodiment, the ablation electrode comprises a hollow electrode formed of a metal sheet defining a plurality of holes. A positional sensor is located in the spaced defined by the hollow electrode. A support flange couples the hollow electrode to a cooling tube with the support flange defining an opening for enabling fluid flow through the opening, then along the positional sensor before exiting the hollow electrode via the defined holes.
A more detailed explanation of the invention is provided in the following description and claims, and is illustrated in the accompanying drawings.